Storage systems may utilize an array of storage devices to provide high performance scale-out storage. A storage system may use various metadata to process I/O operations. Such metadata may be cached in primary memory (e.g., volatile RAM) to avoid accessing relatively slower non-volatile storage devices (e.g., solid-state drives or SSDs). Primary memory may also be used for other purposes, such as maintaining a journal of pending writes. System performance may be limited by primary memory capacity and/or by how primary memory capacity is allocated.